It is planned during the forthcoming grant period to continue our exploration of the three-dimensional forms of the cytoplasmic ground substances, i.e., the microtrabecular lattice (MTL) and its associations with the various elements of the cytoskeleton. Fractional extractions of living cells with various detergents will provide solutes for characterization on electrophoretic gels which in turn will give valuable clues to the composition of the MTL. Preliminary results from investigations along these lines have already been completed and look extremely promising. Toward the same end the structural distribution in the lattice of such well known proteins as tubulin, calmodulin, myosin and actin will be assessed as well with labeled antibodies. It has been demonstrated by one of our collaborators, Dr. Jan DeMay (Brussels), that antibodies can be labeled with colloidal gold and used to great advantage to localize specific antigens mentioned above. This approach will be pursued vigorously within the coming period with both whole cultured cells and with sections cut from differentiated cells embedded in polyethyleneglycol (PEG). It is expected that among other systems we shall examine differentiating myoblasts for the earliest appearance of actin myosin and actinin relative to polysomes and to the microtrabeculae in which these reside. We have already worked out the involvement of these elements in the assembly of myofibrils; it remains only to complete the story with the positive identification of the specific proteins relative to structural elements as they develop in both in vitro and in situ systems. It becomes evident with increasing certainty that the MTL, in which the high voltage microscopy has contributed so impressively, is part of a pan cellular system, which we are calling the cytoplast. It is built around an identifiable center that includes microtubule initiating sites and centrioles. We propose to probe with ultraviolet microbeam surgery the components of this center for the presence of organizational information.